The objectives of this investigation are two fold (a) to ascertain whether a proliferative process involving vascular and perivascular cells of capillaries and arterioles represents the primary event in the pathogenesis of scleroderma (b) to characterize the chemical structure of the collagen in the dermis and subcutaneous tissue. Cell proliferation will be studied "in vitro" by means of light and electron microscopic autoradiography with tritiated thymidine. Fibroblast-like cells characterized by their high content in filaments, 160A in diameter will be studied by immunofluorescence microscopy using antibodies against smooth muscle actomyosin, myosin and actin. Collagen from scleroderma will be chemically characterized by its amino acid composition, glycosylation, solubility properties, cross- linkage, susceptibility to collagenase digestion and cyanogen bromide peptide mapping.